1. Field of the Invention
The present invention relates to a field effect transistor (hereinafter, abbreviated to FET), more particularly to an FET using negative resistance based on the resonant tunneling effect, and a method of manufacturing the FET.
2. Description of the Related Art
An FET having a structure of resonant tunneling diode (hereinafter, abbreviated to RTD) provided between a gate electrode and channel layer has been known as an FET utilizing the resonant tunneling effect. FIG. 6 is a diagrammatically illustrated perspective view showing an FET structure. Such FET has disclosed in the literature reported on Applied Physics Letters by F. Capasso, 1987, vol. No. 51, pp. 526.
Referring to FIGS. 6A and 6B, a reference numeral 60 denotes a GaAs (Gallium/Arsenic) substrate having a semi-insulation, 61 denoting an un-doped GaAs buffer layer, 62 denoting an n-type GaAs channel layer, 63 denoting an RTD structure, and 64 denoting an n-type GaAs contact layer. As shown in FIG. 6A, a source electrode 5S and a drain electrode 5D lie on the n-type GaAs channel layer 62 to thereby have an ohmic contact. In addition, a gate electrode 6b (or an ohmic electrode) also lies on the n-type GaAs contact layer 64 to have an ohmic contact.
Referring to FIG. 6B showing a partially enlarged view indicated by a circle on FIG. 6A, the RTD structure 63 having a stacked structure includes an un-doped GaAs spacer layer 63A, an un-doped AlAs (Aluminum/Arsenic) quantum barrier layer 63B, an un-doped GaAs quantum well layer 63C, an un-doped AlAs quantum barrier layer 63D and an un-doped GaAs spacer layer 63E.
Such FET can be used for a negative resistance amplifier, a negative resistance oscillator and the like since the gate current has negative resistance characteristic.
However, the gate electrode of such FET has an ohmic electrode, therefore, current flows between not only the gate and source, but also the drain and source caused by no rectification of the RTD structure. As a result, the feedback component of current increases to thereby decrease the gain of FET, making its operation unstable.